Add TEST_LOG diagnostics for silent dump/copy failure paths

Profiler::dump() discarded _jfr.dump()'s Error entirely, and
OS::copyFile()'s sendfile() loop broke silently on short/failed
copies - both are debug-only visibility gaps that would otherwise
leave a lost reference-chain write or truncated chunk copy
unexplained in CI logs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/src/main/cpp/flightRecorder.cpp

@@ -851,6 +851,8 @@ void Recording::switchChunk(int fd) {
   _chunk_start = finishChunk(/*end_recording=*/true, /*do_cleanup=*/true);
 
   TEST_LOG("MethodMap: %zu methods after cleanup", _method_map.size());
+  TEST_LOG("Recording::switchChunk copying [0, %lld) from _fd=%d to fd=%d",
+           (long long)_chunk_start, _fd, fd);
 
   _start_time = _stop_time;
   _start_ticks = _stop_ticks;

ddprof-lib/src/main/cpp/os_linux.cpp

@@ -730,9 +730,12 @@ int OS::createMemoryFile(const char* name) {
 
 void OS::copyFile(int src_fd, int dst_fd, off_t offset, size_t size) {
     // copy_file_range() is probably better, but not supported on all kernels
+    size_t requested = size;
     while (size > 0) {
         ssize_t bytes = sendfile(dst_fd, src_fd, &offset, size);
         if (bytes <= 0) {
+            TEST_LOG("OS::copyFile sendfile returned %zd, errno=%d, remaining=%zu of requested=%zu",
+                     bytes, errno, size, requested);
             break;
         }
         size -= (size_t)bytes;

ddprof-lib/src/main/cpp/profiler.cpp

@@ -1850,6 +1850,9 @@ Error Profiler::dump(const char *path, const int length) {
       err = _jfr.dump(path, length);
       __atomic_add_fetch(&_epoch, 1, __ATOMIC_SEQ_CST);
     });
+    if (err) {
+      TEST_LOG("Profiler::dump _jfr.dump failed: %s", err.message());
+    }
 
     _thread_info.clearAll(thread_ids);
     _thread_info.reportCounters();